﻿<p>An advanced B-rep is a boundary representation model in which all faces, edges and vertices are explicitly represented. It is a solid with explicit topology and elementary or free-form geometry. The faces of the B-rep are of type <em>IfcAdvancedFace</em>. An advanced B-rep has to meet the same topological constraints as the manifold solid B-rep.</p>

<blockquote class="note">NOTE&nbsp; The advanced B-rep has been introduced in order to support the increasing number of applications that can define and exchange B-rep models based on NURBS or other b-spline surfaces.</blockquote>

<table summary="faceted brep" border="0">
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<td valign="top"><img src="../../../figures/ifcadvancedbrep_01.png" alt=
"advanced brep b-spline surface" width="600" height="600"></td>
<td style="vertical-align:bottom">
<p>Figure 3 illustrates use of <em>IfcAdvancedBrep</em> for boundary representation models with b-spline surfaces. The diagram shows the topological and geometric representation items that are used for advanced B-reps, based on <em>IfcAdvancedFace</em>.</p>
</td>
</tr>
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<td>
<p class="figure">Figure 3 &mdash; Advanced Brep, b-spline surface</p>
<p>&nbsp;</p>
</td>
<td>&nbsp;</td>
</tr>
<tr>
<td valign="top">&nbsp;&nbsp;&nbsp;<img src="../../../figures/ifcadvancedbrep_02.png" alt=
"advanced brep elementary surface" width="600" height="650"></td>
<td style="vertical-align:bottom">
<p>Figure 4 illustrates use of <em>IfcAdvancedBrep</em> for boundary representation models with elementary surfaces. The diagram shows the topological and geometric representation items that are used for advanced B-reps, based on <em>IfcAdvancedFace</em>. It shows the use of <em>IfcIntersectionCurve</em> to provide the geometric representation of the edge curve both as 3D curve and as u,v pcurve in the parametric space of the adjacent surfaces.</p>
</td>
</tr>
<tr>
<td>
<p class="figure">Figure 4 &mdash; Advanced Brep, elementary surface</p>
</td>
<td>&nbsp;</td>
</tr>
</table>

<blockquote class="note">NOTE&nbsp; Entity adapted from
<strong>advanced_brep_shape_representation</strong> defined in ISO 10303-514.</blockquote>
<blockquote class="history">HISTORY&nbsp; New entity in IFC4</blockquote>

<p class="spec-head">Informal Propositions:</p>
<ol>
<li>each face is a face surface;</li>
<li>each face surface has its geometry defined by an elementary surface, swept surface or a b-spline surface;</li>
<li>the edges used to define the boundaries of the face shall all reference an edge curve</li>
<li>each curve used to define the geometry of the faces and face bounds shall be either a conic, or a line or a polyline or a
b-spline curve</li>
<li>the edges used to define the face boundaries shall all be trimmed by vertices of type vertex point</li>
<li>no loop used to define a face bound shall be of the oriented subtype</li>
</ol>